LED driver with comprehensive fault protections

ABSTRACT

The embodiments disclosed herein describe a set of fault detection circuits for LED circuits in an LED channel. A first fault detection circuit is configured to detect a short fault across one or more LEDs. A second fault detection circuit is configured to detect an open fault across an LED. A third fault detection circuit is configured to detect a short across an LED channel transistor. A fourth fault detection circuit is configured to detect an LED channel sense resistor open fault. A fifth fault detection circuit is configured to detect if the LED channel is being intentionally unused. These fault detect circuits can be implemented in a fault detection integrated circuit coupled to the LED channel.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/787,270, filed Oct. 27, 2015, now U.S. Pat. No. 9,999,110, which isthe National Stage of International Application No. PCT/US2014/042591,filed Jun. 16, 2014, published in English under PCT Article 21(2), whichclaims priority to U.S. Provisional Application No. 61/837,036, filedJun. 19, 2013, the contents of which are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

This invention pertains generally to the field of LED circuits and, moreparticularly, to LED circuit fault detection.

BACKGROUND

Three-dimensional televisions and other displays often requireincreasingly higher current and higher density LED arrays. In someinstances, electrical current flowing through each string of LEDS in anLED array for display backlighting ranges from around 100 mA to 1 A orgreater. In order to address the heat produced by such currents and tolower IC cost, display manufacturers can move heat-producing components,such as power MOSFETs and LED current sensing resistors, off chip.

SUMMARY OF THE INVENTION

The present disclosure describes a set of fault detection circuits forLED circuits. These fault detection circuits can be implemented within afault detection IC. Two such fault detection circuits are an LED shortfault detection circuit and an LED open fault detection circuit. Inaddition, the fault detection IC can include a MOSFET drain-to-sourceshort fault detection circuit, a sense resistor open fault detectioncircuit, a sense resistor short fault detection circuit, and an LEDchannel short detection circuit. The fault detection IC can furtherinclude circuitry configured to determine if a particular LED channel isunused. The fault detection IC can include circuits configured to act asa first type of fault detection circuit in a calibration mode, and as asecond type of fault detection circuit in an operation mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an LED driver circuit, according to one embodiment.

FIG. 2 illustrates a connector array on a PCB with a short betweenadjacent connector nodes, according to one embodiment.

FIG. 3 illustrates a set of fault detection circuits for use in LEDcircuits, LED driver circuits, and LED channels, according to oneembodiment.

FIG. 4 illustrates a timing diagram for fault detection circuits duringa calibration mode, according to one embodiment.

FIG. 5 illustrates a logic table for use in detecting faults in acalibration mode, according to one embodiment.

FIG. 6 illustrates an LED channel short circuit fault detection circuit,according to one embodiment.

DETAILED DESCRIPTION

The Figures (Figs.) and the following description relate to variousembodiments by way of illustration only. Reference will now be made indetail to several embodiments, examples of which are illustrated in theaccompanying figures. It is noted that wherever practicable similar orlike reference numbers may be used in the figures and may indicatesimilar or like functionality. The figures depict various embodimentsfor purposes of illustration only. One skilled in the art will readilyrecognize from the following description that alternative embodiments ofthe structures and methods illustrated herein may be employed withoutdeparting from the principles described herein.

FIG. 1 shows an LED driver circuit, according to one embodiment. Thedriver circuit of FIG. 1 includes MOSFET 100, amplifier 105, and senseresistor R_(SENSE). The positive input terminal of the amplifier 105 iscoupled to an input V_(ADIM), and the negative input terminal of theamplifier is coupled to the source node of the MOSFET 100. An LED string110 is coupled between the voltage source WED and the drain node of theMOSFET 100.

The output of the amplifier 105 is coupled to the gate node of theMOSFET 100. The amplifier 105 outputs a signal based on the differencebetween signals received at the positive and negative input terminals ofthe amplifier. In one embodiment, the amplifier 105 is a high gainamplifier. The input V_(ADIM) controls the switching of the gate node ofthe MOSFET 100.

When the output of the amplifier 105 is high, the MOSFET 100 acts as aclosed switch. In such a configuration, current flows from the voltagesource V_(LED), through the LED string 110 (causing the LEDs to emitlight), through the drain node of the MOSFET 100 to the source node ofthe MOSFET, and through the resistor R_(SENSE). When the output of theamplifier 105 is low, the MOSFET 100 acts as an open switch, preventingcurrent from flowing from the voltage source V_(LED) through the MOSFET(and thus preventing the LEDs from emitting light).

In the embodiment of FIG. 1, the resistor R_(SENSE) is generally alow-resistance resistor. For example, the resistance of R_(SENSE) may beequal to or less than 2Ω. The voltage across R_(SENSE) (V_(SENSE)) isused as a feedback signal to control the output of the amplifier 105,which in turn controls the switching of the MOSFET 100 and the currentthrough the LED string 110.

In one example embodiment, V_(LED) is 70V and the LED string 110includes 20 LEDs. In this embodiment, when current is flowing throughthe MOSFET 100, the voltage drop across each LED is approximately 3.3V.As a result, the voltage at the drain node of the MOSFET 100 isapproximately 4V.

Manufacturing defects and gradual degradation over time can occur withinoff-chip MOSFETs, LED current sensing resistors, and other off-chipcomponents. One or more LEDs in the LED string 110 can be shorted oropened. Shorted LEDs can be particularly problematic, as they can causeadditional LEDs to become shorted, and can cause over-heating on anexternal MOSFET 100. In addition, the source and drain nodes of theMOSFET 100 can be shorted. Further, the nodes of the sensing resistorR_(SENSE) can shorted or opened. Traditional on-chip LED short and opencircuit protections generally fall short of addressing such defects foroff-chip components.

In addition, individual LED channels can be shorted. FIG. 2 illustratesa connector array on a PCB with a short between adjacent connector nodes1 and 2. If an LED string A is coupled to node 1, and an LED string B iscoupled to node 2, the power circuit used to control current flowthrough LED string A can additionally cause current to flow through LEDstring B. Thus, fault detection and prevention is necessary for LEDchannel shorts as well.

As noted above, the present disclosure describes fault detectioncircuits for use with LED circuits and LED power circuits. It should benoted that in other embodiments, the described circuits can be used inconjunction with other circuits, systems, and devices. The faultdetection circuits can detect the presence of one or more types ofcircuit faults either before circuit operation (for instance, during acalibration mode) or in real-time during circuit operation. Suchflexibility can optimize the likelihood that a fatal circuit fault isdetected, and can help reduce the likelihood of damaging the circuit ora related circuit or system.

FIG. 3 illustrates a set of fault detection circuits for use in LEDcircuits, LED driver circuits, LED channels, and any other suitable LEDcircuit, according to one embodiment. In the embodiment of FIG. 3, thefault detection circuits are included on a single IC 120, though itshould be noted that in other embodiments, the fault detection circuitscan be included on separate ICs, or can be implemented in othercontexts. Further, it should be noted that in other embodiments, thefault detection IC 120 only includes a subset of the fault detectioncircuits described herein. In the embodiment of FIG. 3, the faultdetection IC 120 is coupled to an LED channel 115 made up of the LEDstring 110, the MOSFET 100, and the sense resistor R_(Sense). It shouldbe noted that although the term “fault detection IC” is used, it shouldbe noted that the fault detection functionality described herein can beincorporated into other circuits, such as LED driver circuits, or can beimplemented in standalone circuits.

The fault detection IC 120 can include an LED short detection circuitconfigured to detect LED short circuit faults. The LED short detectioncircuit includes a voltage divider, made up of R₁ and R₂, and acomparator 140. The LED short detection circuit detects shorts acrossone or more LEDs in the LED string 120. The voltage divider is coupledto the drain node of the MOSFET 100. As noted above, the voltage at thedrain node of the MOSFET 100 is equal to the difference between thesource voltage V_(LED) and the cumulative voltage drops over the LEDs inthe LED string 110.

The comparator 140 receives the voltage divider voltage V_(DIV) and areference voltage V_(Ref1), compares the two voltages, and outputs anerror signal LED_short based on the comparison. The values of theresistors R₁ and R₂ can be selected to reduce the voltage at the drainnode of the MOSFET 100 by a pre-determined percentage. The referencevoltage V_(Ref1) can be selected to satisfy the following twoconditions:

-   -   1. V_(Ref1)<V_(DIV) if one or more LEDs in the LED string 110 is        shorted, and    -   2. V_(Ref1)>V_(DIV) if no LEDs in the LED string 110 are shorted

For example, if one or more LEDs in the LED string 110 are shorted, thevoltage drop across the LED string will decrease, resulting in a greatervoltage at the drain node of the MOSFET 100 than if no LEDs wereshorted. The comparator 140 detects such a higher voltage by comparingthe voltage V_(DIV), which is based on the drain voltage of the MOSFET100, to reference voltage V_(Ref1), and outputs an error signalLED_short if V_(DIV)/>V_(Ref1). It should be noted that the LED shortdetection circuit can beneficially detect LED short circuit faultsduring real-time operation of the LED string 110 and MOSFET 100.

The fault detection IC 120 can include an LED open detection circuitconfigured to detect LED open circuit faults. The LED open detectioncircuit includes a comparator 144. The comparator 144 receives thevoltage at the source node of the MOSFET 100 and a reference voltageV_(Ref3), compares the two voltages, and outputs an error signalLED_open based on the comparison. In the event of an LED open circuitfault condition, no current flows through LED channel 115 (from thesource voltage V_(LED) through the MOSFET 100 and the sense resistorR_(sense)). When current is not flowing through the sense resistorR_(sense), there is no voltage drop across R_(sense), and the voltage atthe source node of the MOSFET 100 is zero.

The reference voltage V_(Ref3) can be selected to satisfy the followingtwo conditions:

-   -   1. V_(Ref3)>0, and    -   2. V_(Ref3)<V_(Source) during normal operation of LED string 110        (no open circuit fault)

The comparator 144 is configured to output the error signal LED_openwhen the voltage V_(Source) is less than the reference voltage V_(Ref3).For example, if current is flowing from the source voltage V_(LED)through the LED string 110 and the MOSFET 100, the voltage V_(Source) isequal to the product of the current and the resistance of R_(sense). Ifthe current flowing through the MOSFET 100 is 1 A and the resistance ofR_(sense) is 2Ω, then V_(Source) is 2V. If V_(Ref3) is selected to be1V, then the comparator 144 will output the error signal LED_open whenno current is flowing through the MOSFET 100 (since V_(Source) will be0V, less than the 1V reference voltage), and will not output the errorsignal when the 1 A current is flowing through the MOSFET (sinceV_(Source) will be 2V, greater than the 1V reference voltage). It shouldbe noted that the LED open detection circuit can beneficially detect LEDopen circuit faults during real-time operation of the LED string 110 andthe MOSFET 100.

The fault detection IC 120 can include a MOSFET short detection circuitconfigured to detect a short circuit fault between the source and drainnodes of the MOSFET 100. The MOSFET short detection circuit includes thecomparator 142. If the drain and source nodes of the MOSFET 100 areshorted, current continuously flows from the source voltage V_(LED) andthrough the LED string 110 and resistor R_(sense). In such instances,the voltage V_(Sense) stays higher than V_(ADIM), and the high-gainamplifier 105 outputs the voltage V_(Gate), which reflects thecontinuously high voltage V_(Sense). Accordingly, V_(Gate) tends towards0V, lower than the voltage V_(Gate) required to cause the MOSFET 100 toact as an open circuit in normal operation.

The comparator 142 receives the voltage V_(Gate) and the referencevoltage V_(Ref2), compares the two voltages, and outputs an error signalDS_short based on the comparison. The reference voltage V_(Ref2) can beselected to satisfy the following two conditions:

-   -   1. V_(Ref2)>V_(Gate) when V_(Sense) stays high (as a result of a        short circuit fault between the drain and source nodes of MOSFET        100), and    -   2. V_(Ref2)<V_(Gate) during normal operation of MOSFET 100 (the        voltage required to configure the MOSFET to act as an open        switch)

The comparator 142 is configured to output the error signal DS_shortwhen the voltage V_(Ref2) is greater than the voltage V_(Gate). Itshould be noted that the MOSFET short detection circuit can beneficiallydetect short circuit faults between the drain node and the source nodeof the MOSFET 100 during real-time operation of the MOSFET 100.

The fault detection IC 120 can include a sense resistor short detectioncircuit configured to detect a short circuit fault across R_(Sense). Thesense resistor short detection circuit includes a comparator, and in oneembodiment, includes the comparator 144. When a short circuit faultexists across R_(Sense), the voltage drop across R_(Sense) is 0V. Thisis a similar result to an LED open circuit fault—both result in a 0Vpotential across R_(Sense). Accordingly, the same comparator can be usedto detect both faults. V_(Ref3) can be selected to satisfy the same twoconditions discussed above, and the comparator 144 can output the errorsignal R_(Sense_)short in response to a determination thatV_(Source)<V_(Ref3). It should be noted that in other embodiments, thesense resistor short detection circuit and the LED open circuit detectorcan each include a separate comparator. Further, the sense resistorshort detection circuit can beneficially detect sense resistor shortcircuit faults during the real-time operation of the MOSFET 100.

The fault detection IC 120 can include a sense resistor open detectioncircuit configured to detect an open circuit fault across R_(Sense).When R_(Sense) includes an open circuit fault, current cannot flowthrough the LED channel 115. The fault detection IC 120 can also includean unused LED channel detection circuit configured to detect if the LEDchannel 115 is unused. If an LED channel is to be unused, the senseresistor R_(Sense) (generally ˜2Ω or less) can be replaced with a muchlarger resistor, for example 100 kΩ or more. Both unused channels andsense resistor open circuit faults prevent enough current from flowingthrough the LEDs in the LED channel 120 to cause the LEDS to emit light.

In one embodiment, the sense resistor open detection circuit and theunused LED channel detection circuit are implemented by the samecircuit. In addition, in some embodiments, the sense resistor opendetection circuit and the unused LED channel detection circuit detectopen circuit faults and unused LED channels, respectively, beforereal-time operation of the LED channel 115, for instance in acalibration mode. In such embodiments, such as the embodiment of FIG. 3,the sensor resistor open detection circuit and the unused LED channeldetection circuit can also be implemented in the same circuit as the LEDopen detection circuit described above. It should be noted that in otherembodiments, the sense resistor open detection circuit, the unused LEDchannel detection circuit, and the LED open detection circuit can beimplemented in separate circuits.

The sense resistor open detection circuit and the unused LED channeldetection circuit include the comparator 144, the comparator 146, theMOSFET 130, the current source I_(Ref), the input V_(Cal), and thedecoder 148. The comparator 144 receives the voltage at the source nodeof the MOSFET 100, V_(Source), compares it to the reference voltageV_(Ref3), and outputs a signal c1 based on the comparison. Since thedetection of sense resistor open circuit faults and unused LED channelsoccurs in a calibration mode (or any other mode prior to real-timeoperation of the LED channel 115), the value of V_(Ref3) used by thecomparator 144 can be different than the value of V_(Ref3) used whendetecting LED open circuit faults. The comparator 146 receives thevoltage V_(Source), compares it to the reference voltage V_(Ref4), andoutputs a signal c2 based on the comparison.

During the calibration mode, the input V_(Cal) goes high, configuringthe MOSFET 130 to act as a closed switch, causing the current I_(Ref) toflow through the MOSFET 130. In embodiments where R_(Sense) includes anopen circuit fault, the voltage V_(Source) becomes equal to V_(Test).For example, V_(Test) can be 5V. In embodiments wherein the LED channel115 is unused, the voltage V_(Source) is equal to I_(Ref)*R_(sense). Forexample, if I_(Ref)=10 μA and R_(sense)=100 kΩ, then V_(Source)=1V.

FIG. 4 illustrates a timing diagram for the fault detection circuits ofthe fault detection IC 120 during a calibration mode, according to oneembodiment. Calibration mode begins at time t1. At t1, V_(Cal) goes highfor a period of 32 μs. During this time interval, V_(ADIM) stays low,preventing operation of the LED channel 115. When V_(Cal) is high, thecomparators 144 and 146 produce signals c1 and c2, respectively, and thedecoder 148 produces a channel status signal based on c1 and c2. At timet2, V_(Cal) goes low, marking the end of calibration mode. After aperiod of 32 μs, at time t3, V_(ADIM) goes high, and the LED channel 115operates in a normal mode. It should be noted that the periods of timeselected herein for calibration mode are merely exemplary, and can bedifferent in other embodiments.

In one embodiment, the reference voltage V_(Ref3) can be selected tosatisfy the following two conditions:

-   -   1. V_(Ref3)<I_(Ref)*R_(sense) when R_(Sense)>1 kΩ, and    -   2. V_(Ref3)>I_(Ref)*R_(sense) when R_(Sense)<1 kΩ

The comparator 144 is configured to output the signal c1 as high whenV_(Source)>V_(Ref3), and to output the signal c1 as low whenV_(Source)<V_(Ref3). Continuing with the previous example, ifI_(Ref)*R_(sense)=1V when R_(sense)=100 kΩ and if I_(Ref)*R_(sense)=20μV when R_(sense)=2Ω, then selecting V_(Ref3)=0.5V will result in thecomparator 144 outputting c1 as high when the LED channel is unused, andoutputting c1 as low when the LED channel is used. It should be notedthat V_(Ref3), as well as any of the reference voltages describedherein, can be selected according to other criteria than those describedherein.

In one embodiment, the reference voltage V_(Ref4) can be selected tosatisfy the following two conditions:

-   -   1. V_(Ref4)<V_(Test), and    -   2. V_(Ref4)>I_(Ref)*R_(sense) when R_(Sense)≥100 kΩ

The comparator 146 is configured to output the signal c2 as high whenV_(Source)>V_(Ref4), and to output the signal c2 as low whenV_(Source)<V_(Ref4). Continuing with the previous example, if V_(Test)=5v, V_(Ref4)=4.5V, and R_(Sense) is open, then V_(Source)=V_(Test), andthe comparator will determine that V_(Source)>V_(Ref4), outputting c2 ashigh. Likewise, if R_(Sense)<100 kΩ, then the comparator will determinethat V_(Source)<V_(Ref4), outputting c2 as low.

The decoder 148 is configured to receive the signal c1 and c2, and isconfigured to output the signal channel_status in response to the valuesof c1 and c2. FIG. 5 illustrates a logic table for use by the decoder148 in detecting faults in a calibration mode, according to oneembodiment. When c1 and c2 are low, the output signal channel_statusindicates that no fault is detected, and that the LED channel 115 is inuse (for example, R_(Sense)≤2Ω). When c1 is high and c2 is low, theoutput signal indicates that the LED channel 115 is not intentionally inuse (for example, R_(Sense)>100 kΩ). When c1 is low and c2 are high, theoutput signal indicates that a fault is detected, and that R_(Sense)includes an open circuit. In other embodiments, the comparators 144 and146 can output c1 and c2, respectively, according to different criteriathan those described herein, and the decoder 148 can output differentchannel_status signals in response to different criteria or differentinputs than those described herein.

The fault detection IC 120 can include an LED channel short detectioncircuit configured to detect short circuit faults between LED channels,for instance at the PCB level. FIG. 6 illustrates an LED channel shortcircuit fault detection circuit, according to one embodiment. Theembodiment of FIG. 6 includes two LED channels, channel 1 and channel 2.Each LED channel includes a string of LEDs, a MOSFET, and a senseresistor. The gate of the MOSFET of channel 1 is coupled to theamplifier 155, which receives input signal V₁. The gate of the MOSFET ofchannel 2 is coupled to the amplifier 150, which receives input signalV₂.

The LED channel short detection circuit of FIG. 6 includes thecomparator 160, which is configured to receive the gate voltage of theMOSFET of channel 1 (V_(Drain1)), and the reference voltage V_(Ref1).The comparator 160 is further configured to compare V_(Drain1) andV_(Ref1), and to output the signal channel_short_1 in response to thecomparison. Similarly, the LED channel short detection circuit of FIG. 6includes the comparator 162, which is configured to receive the gatevoltage of the MOSFET of channel 2 (V_(Drain2)), and the referencevoltage V_(Ref2). The comparator 162 is further configured to compareV_(Drain2) and V_(Ref2), and to output the signal channel_short_2 inresponse to the comparison. It should be noted that in some embodimentsthe reference voltages V_(Ref1) and V_(Ref2) are the same voltage. Inaddition, in some embodiments, the signals channel_short_1 andchannel_short_2 are the same signal (as a short between channel 1 andchannel 2 is detectable by either comparator 160 or 162).

In the embodiment of FIG. 6, channel 1 and channel 2 include a shortcircuit fault 165, which couples the drain node of the MOSFET of channel1 (D₁) to the drain node of the MOSFET of channel 2 (D₂). The shortcircuit fault 165 in the embodiment of FIG. 6 is shown external to thefault detection IC (for instance, at the PCB level), but it should benoted that in some embodiments, short circuit faults between LEDchannels can be internal to the fault detection IC. The short 165 causesthe voltage on the drain nodes of the MOSFETs to be the same. Inembodiments without the short 165, for example, when V₂ is high and V₁is low, the MOSFET of channel 2 is configured to act as a closed switchand the MOSFET of channel 1 is configured to act as an open switch.Accordingly, current is configured to flow through channel 2, but notchannel 1. In such circumstances, the voltage at the drain of the MOSFETof channel 1 is equivalent to the LED supply voltage V_(C1), since nocurrent is flowing through channel 1. In embodiments with the short 165,current can flow through the LED string of channel 1, through the short165, and through the MOSFET of channel 2. In such circumstances, thevoltage at the drain node of the MOSFET of channel 1 is lower than if nocurrent were flowing through the LED string of channel 1.

In one embodiment, the reference voltage V_(Ref1) can be selected tosatisfy the following two conditions:

-   -   1. V_(Ref1)<V_(C1), and    -   2. V_(Ref1)>V_(Drain1) when current is flowing through the        MOSFET of channel 1 (for instance, when V₁ is high)

Similarly, in one embodiment, the reference voltage V_(Ref2) can beselected to satisfy the following two conditions:

-   -   1. V_(Ref2)<V_(C2), and    -   2. V_(Ref2)>V_(Drain2) when current is flowing through the        MOSFET of channel 2 (for instance, when V₂ is high)

Referring to fault detection embodiments by channel 1, the comparator160 compares V_(Ref1) and V_(Drain1), outputs channel_short_1 as high ifV_(Drain1)<V_(Ref1) (indicating the presence of short 165), and outputschannel_short_1 as low if V_(Drain1)>V_(Ref1) (indicating that no shortis detected between channels). Referring to fault detection embodimentsby channel 2, the comparator 162 can output channel_short_2 similarlybased on a comparison of V_(Drain2) and V_(Ref2). The detection ofshorts between LED channels can occur before operation, for instance inthe calibration mode described above or during PCB manufacture.Accordingly, the LED channel short detection circuit and the LED shortdetection circuit described above can be implemented with the samecomparator. For example, the comparator 140 of FIG. 3 and the comparator160 of FIG. 6 can be the same comparator. In such embodiments, thereference voltages V_(Ref1) of FIG. 3 and V_(Ref1)/V_(Ref2) of FIG. 6can be different, and can change based on the mode of operation(calibration mode vs. normal mode). It should be noted that incalibration mode, every combination of LED channel pairs in an LEDchannel array can be individually tested as described herein to detectthe presence of a short between any two LED channels.

Upon reading this disclosure, those of skill in the art will appreciatestill additional alternative designs for controlling the dimmingoperation of an LED. Thus, while particular embodiments and applicationshave been illustrated and described, it is to be understood that theembodiments discussed herein are not limited to the precise constructionand components disclosed herein and that various modifications, changesand variations which will be apparent to those skilled in the art may bemade in the arrangement, operation and details of the method andapparatus disclosed herein without departing from the spirit and scopeof the disclosure.

What is claimed is:
 1. An LED fault detection circuit configured todetect one or more faults of an LED channel comprising one or more LEDscoupled to a drain node of a transistor and a resistor coupled to asource node of the transistor, the circuit comprising: a first faultdetection circuit coupled to the source node of the transistor andconfigured to: when the LED fault detection circuit is operating in anoperating mode, detect an open fault within the one or more LEDs; andwhen the LED fault detection circuit is operating in a calibration mode,detect a short fault across the resistor, wherein the LED faultdetection circuit is configured to operate in the calibration modebefore being configured to operate in the operating mode; and a secondfault detection circuit comprising a comparator, a second transistor,and a current source coupled to a drain node of the second transistor,the second fault detected circuit coupled to the source node of thetransistor and configured to detect an open fault across the resistorby, when the second transistor is configured to operate as a closedswitch, comparing the voltage at the source node of the transistor to areference voltage and outputting a fault signal indicating a presence orabsence of the open fault across the resistor based on the comparison.2. The LED fault detection circuit of claim 1, further comprising athird fault detection circuit configured to detect a short fault acrossone or more of the LEDs, the third fault detection circuit coupled tothe drain node of the transistor.
 3. The LED fault detection circuit ofclaim 2, wherein the third fault detection circuit comprises a voltagedivider coupled to the drain node of the transistor, the voltage dividercomprising a first resistor and a second resistor coupled at a firstnode, the third fault detection circuit further comprising a comparatorcoupled to the first node.
 4. The LED fault detection circuit of claim3, wherein the comparator is configured to compare a voltage at thefirst node to a reference voltage and to output a fault signalindicating the presence or absence of a short fault across one or moreof the LEDs based on the comparison.
 5. The LED fault detection circuitof claim 1, wherein the first fault detection circuit comprises acomparator coupled to the source node of the transistor.
 6. The LEDfault detection circuit of claim 5, wherein the comparator is configuredto, when the LED fault detection circuit is operating in an operatingmode, compare a voltage at the source node of the transistor to areference voltage and to output a fault signal indicating the presenceor absence of an open fault within the one or more LEDs based on thecomparison.
 7. The LED fault detection circuit of claim 1, furthercomprising a third fault detection circuit configured to detect a shortfault across the drain node and the source node of the transistor, thethird fault detection circuit coupled to the gate node of thetransistor.
 8. The LED fault detection circuit of claim 7, wherein thethird fault detection circuit comprises a comparator coupled to the gatenode of the transistor.
 9. The LED fault detection circuit of claim 7,wherein the comparator is configured to compare a voltage at the gatenode of the transistor to a reference voltage and to output a faultsignal indicating the presence or absence of a short fault across thedrain node and the source node of the transistor based on thecomparison.
 10. The LED fault detection circuit of claim 1, furthercomprising: a fourth fault detection circuit configured to detect anunused LED channel, the fourth fault detection coupled to the sourcenode of the transistor.
 11. The LED fault detection circuit of claim 10,the fourth fault detection circuit comprising: a second comparatorcoupled to the source node of the transistor, wherein the secondcomparator is configured to, when the transistor is configured tooperate as an open switch and when the second transistor is configuredto operate and when the second transistor is configured to operate as aclosed switch, compare the voltage at the source node of the transistorto a second reference voltage greater than a reference voltage, and tooutput a second fault signal indicating that the LED channel is used orunused.
 12. The LED fault detection circuit of claim 11, furthercomprising: a decoder coupled to the comparator and to the secondcomparator and configured to receive the fault signal and the secondfault signal, and to output a status signal indicative of a state of theLED channel.
 13. An LED fault detection integrated circuit configured todetect faults of an LED channel, the integrated circuit comprising: afirst set of fault detection circuits coupled to a source node of an LEDchannel transistor and configured to detect one or more LED channelfaults when the integrated circuit is configured in a calibration mode;and a second set of fault detection circuits configured to detect one ormore LED channel faults when the integrated circuit is configured in anoperating mode, wherein the integrated circuit is configured to operatein the calibration mode before being configured to operate in theoperating mode; wherein a fault detection circuit is included in thefirst set of fault detection circuits and the second set of faultdetection circuits, and wherein the fault detection circuit isconfigured to detect a sense resistor short circuit fault when theintegrated circuit is configured in the operating mode and to detect anLED open circuit fault when the integrated circuit is configured in thecalibration mode; and wherein the second set of fault detection circuitscomprises a comparator coupled to the gate node of the LED channeltransistor, the comparator configured to compare a voltage at the gatenode of the LED channel transistor to a reference voltage and to outputa fault signal indicating the presence or absence of a short faultacross the drain node and the source node of the LED channel transistorbased on the comparison.
 14. The LED fault detection integrated circuitof claim 13, the first set of fault detection circuits comprising: asecond fault detection circuit configured to detect an open fault at thesource node of the LED channel transistor, the second fault detectioncircuit comprising: a second transistor, the source node of the secondtransistor coupled to the source node of the LED channel transistor; acurrent source coupled to a drain node of the second transistor; and asecond comparator coupled to a source node of the LED channeltransistor, the second comparator configured to compare a voltage at thesource node of the LED channel transistor to a reference voltage and tooutput a second fault signal indicating the presence or absence of anopen fault at the source node of the LED channel transistor.
 15. The LEDfault detection integrated circuit of claim 13, the first set of faultdetection circuits further comprising: a second fault detection circuitconfigured to detect an unused LED channel, the second fault detectioncircuit comprising: a second comparator coupled to the source node ofthe LED channel transistor, the second comparator configured to comparethe voltage at the source node of the LED channel transistor to areference voltage and to output a second fault signal indicating thatthe LED channel is used or unused.
 16. The LED fault detectionintegrated circuit of claim 13, further comprising: a decoder coupled tothe first set of fault detection circuits and configured to output astatus signal indicative of a state of the LED channel based on faultsignals received from the first set of fault detection circuits.
 17. TheLED fault detection integrated circuit of claim 13, wherein the secondset of fault detection circuits further comprises: a second faultdetection circuit comprising: a second comparator coupled to the sourcenode of the LED channel transistor, the second comparator configured tocompare the voltage at the source node of the transistor to a referencevoltage and to output a second fault signal indicating the presence orabsence of an open fault within the one or more LEDs based on thecomparison.
 18. An LED fault detection integrated circuit configured todetect faults of an LED channel, the integrated circuit comprising: afirst set of fault detection circuits coupled to a source node of an LEDchannel transistor and configured to detect one or more LED channelfaults when the integrated circuit is configured in a calibration mode;and a second set of fault detection circuits configured to detect one ormore LED channel faults when the integrated circuit is configured in anoperating mode, wherein the integrated circuit is configured to operatein the calibration mode before being configured to operate in theoperating mode; wherein a fault detection circuit is included in thefirst set of fault detection circuits and the second set of faultdetection circuits, and wherein the fault detection circuit isconfigured to detect a sense resistor short circuit fault when theintegrated circuit is configured in the operating mode and to detect anLED open circuit fault when the integrated circuit is configured in thecalibration mode; and wherein a second fault detection circuit in thefirst set of fault detection circuits is configured to detect an openfault at the source node of the LED channel transistor and comprises: asecond transistor, the source node of the second transistor coupled tothe source node of the LED channel transistor; a current source coupledto a drain node of the second transistor; and a comparator coupled to asource node of the LED channel transistor, the comparator configured tocompare a voltage at the source node of the LED channel transistor to areference voltage and to output a fault signal indicating the presenceor absence of an open fault at the source node of the LED channeltransistor.